1. Field of the Invention
The application relates to a method in a wireless communication system and related communication device, and more particularly, to method of reducing overload in a data base in a wireless communication system.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3GPP Rel-8 standard and/or the 3GPP Rel-9 standard is developed by the 3rd Generation Partnership Project (3GPP) as a successor of a universal mobile telecommunications system (UMTS), for further enhancing performance of the UMTS to satisfy users' increasing needs. The LTE system includes a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved UTRAN (E-UTRAN) includes multiple evolved NBs (eNBs) for communicating with multiple user equipments (UEs), and communicates with a core network including a mobility management entity (MME), serving gateway, etc for Non Access Stratum (NAS) control. In UMTS system, a Serving GPRS Support Node (SGSN) is responsible for the delivery of data packets to the mobile devices back and forth within its geographical service area, including packet routing and transfer, mobility management (attach/detach and location management), logical link management, and authentication and charging functions. The MME also provides the control plane function for mobility between LTE and 2G/3G access networks with the S3 interface terminating at the MME from the SGSN.
An access point name (APN) is used in the LTE system and the LTE-A system for establishing packet data connections, and is managed by the MME. Further, the APN is used for identifying a packet data network (PDN) or a service type (e.g. multimedia messaging service (MMS)), wherein the PDN or the service type is carried on the packet data connections.
NAS level congestion control contains the functions: “APN based congestion control” and “General NAS level Mobility Management control”. The use of the APN based congestion control is for avoiding and handling of congestion associated with a particular APN. Both UEs and network shall support the functions to provide APN based congestion control. With General NAS level Mobility Management control, the MME may also use the reject of NAS level Mobility Management signaling requests under general congestion conditions.
The MME may store a Mobility Management back-off time and a Session Management back-off time when congestion control is active for general NAS MM congestion control or APN based SM congestion control. The MME may enforce the stored back-off time by immediately rejecting any subsequent request from the UE targeting at connecting to the APN before the stored back-off time is expired.
The MME may reject the PDN Connectivity Request with a Session Management back-off timer for congested APNs. If UE provides no APN, then default APN from subscription data is used by the MME. A PDN Gateway (GW) may provide mechanisms for avoiding and handling overload situations. These include the rejection of PDN connection requests from UEs.
When performing overload control the PDN GW rejects PDN connection requests. When receiving the rejection from the PDN GW, the MME rejects the UE's PDN connection request as specified in clause 4.3.7.4.2. of 3GPP.
Due to the rejected UEs perform back-off, the associated service-related entity, e.g. application server, may request the HSS/HLR to provide the reachabilities of the UEs. The HSS/HLR thus sets URRP-MME/URRP-SGSN parameter for each queried UE and sends this parameter to the MME/SGSN via UE-REACHABILITY-NOTIFICATION-REQUEST message. With this request message, the MME/SGSN sets the URRP-MME parameter in the MM Context to monitor the queried UE activity.
The problem is caused when the MME blocks massive UEs with long back-off timers. There may have massive queries from the associated service-related entities to the HSS/HLR which results in HSS/HLR overload. This is because the HSS/HLR has to store massive queries and signal the queries to the registered MME/SGSN. Then the MME/SGSN sets URRP-MME parameters in MM Context of each queried UE. The overload problem may propagate from the HSS/HRL to the MME/SGSN even when the rejected but queried UEs which have MM context in the MME/SGSN do not have any activities due to back-off.